Dbx 162SL

Photo: Mark Ewing

Despite being both smaller and lighter, this new compressor yields little in performance to Dbx's flagship 160SL.

The name Dbx is pretty much synonymous with dynamic control in one form or another, and one of the latest products to emerge is the 162SL dual-channel compressor/limiter — a derivative of the flagship 160SL unit (reviewed in 160S form in SOS January 1998). This new unit has been designed to retain as much of the sonic transparency of the 160SL as possible, while retaining the same intuitive user interface and sophisticated dynamic control, but at a price which will appeal more to the live-sound and home-studio markets. The 162SL doesn't quite match the superb technical specifications of the 160SL, but it doesn't give that much away either — and the compromise is a very fair one given the price advantage.

Building on the heritage of earlier classic Dbx products, the 162SL provides the same automatic attack/release and hard-knee threshold characteristics of the original Dbx 160 model, plus the Auto Velocity manual mode from the revised 160SL model. It also incorporates the famous Overeasy characteristic first seen on the Dbx 165A, and the dual-stage Peak Stop Plus limiting algorithm. Like any dynamics processor the core element is the variable gain stage, and the 162SL uses similar VCA technology to that in the 160SL, based on a design developed from the late Dbx founder David Blackmer's original 'decilinear VCA'. This new implementation is claimed to provide an exceptional dynamic range capability (up to 127dB) allied with extremely low distortion.

Like the 160SL, high-quality components are used throughout the 162SL, including Jensen output transformers, sealed relays with gold contacts, and a custom-machined quarter-inch-thick aircraft-grade-aluminium front panel. So, construction quality and reliability can be assumed to be on a par with the 160SL, yet this new model is almost half the weight (5.1kg instead of 9.3kg) and the case is only 10 inches deep (instead of 11.25). The weight and space savings come from a simpler power supply, much more compact VCA stages, and a general condensation of the circuitry.

Interfacing

The rear panel features parallel-wired XLR and TRS sockets for both inputs and outputs — all balanced, and with an earth-lift facility for the input side on both channels. Nominal signal levels can be switched between +4dBu and -10dBV independently on each channel. The inputs are electronically balanced, while the outputs employ Jensen transformers — but both interfaces can accommodate unbalanced connections without problems. The input impedance is a tad higher than that of the 160SL (50kΩ instead of 20kΩ), and the output impedance a little lower (30Ω instead of 50Ω) — both of which reflect circuit changes — but neither change will cause problems and both provide more universally acceptable interface conditions.

Further pairs of TRS sockets provide balanced side-chain insert send and return facilities for each channel. It is quite unusual to have separate sockets for this function, let alone balanced signals at sensible levels, but it's very welcome if you want to hook the unit up through a patchbay.

The remaining rear-panel facilities are an IEC mains inlet socket with integral fuse and voltage selector, and the mains power switch. This may cause a degree of frustration for some if the 162SL is rackmounted, as reaching the power switch might become rather difficult.

Photo: Mark Ewing

Front-panel Controls

If it weren't for the purple panel, the unit would be impossible distinguish visually from the 160SL model — such is the similarity in layout and control functions. The two channels feature identical groups of six rotary controls alongside a small square VU meter and a collection of buttons — all of which look and feel solid and reliable.

The top three rotary controls adjust the compression Threshold (-40dBu to +20dBu), the compression ratio (labelled Compression and scaled from 1:1 to infinity:1) and Output Gain (±20dB). The last control can be used both to provide make-up gain after compression, and to reduce the unit's output level to suit semi-professional equipment or consoles. The Compression control is the largest knob, with the Threshold and Output Gain knobs being slightly smaller, but still larger than the three controls below — the size differentiation is a great help in navigating the control panel. The 162SL uses RMS detection for the side-chain and so reacts to the average signal level more than the instantaneous peak levels — making it better suited to creative applications rather than protective ones. Not that that will come as a surprise to anyone!

Above and to the right of the Output Gain control is a red peak overload LED calibrated to illuminate at +21dBu (3dB below the actual clip point of the unit). Above the Threshold control is a trio of LEDs, coloured green, yellow, and red. By default, the unit operates with a hard knee and the yellow LED is disabled. The green LED illuminates when the input signal is below the threshold (and thus the compressor is inactive), while the red light is triggered when the threshold is exceeded and some degree of compression is being applied. This arrangement makes it very easy to set the required threshold visually, as it becomes very obvious where the threshold is placed relative to the sound source's dynamics.

The famous Overeasy mode is activated with a button adjacent to the Threshold knob, and this introduces a soft-knee characteristic to the compression threshold. In this mode the yellow LED above the control becomes active and indicates when the input signal is within the soft-knee zone, switching to the green LED when the input falls below the Overeasy zone, and red when rising above it. Again, this makes setting the appropriate threshold very easy, in addition to providing a clear indication of when the Overeasy mode is engaged.

The three lower rotary controls adjust the attack and release times, as well as the separate peak-limiter threshold. The Attack control is calibrated in an unusually technical manner: rather than simply quoting some arbitrary time value, Dbx list the technically precise response time in decibels per millisecond or second. In this case, the Attack control ranges from 400dB/ms (very fast) to 1dB/ms (slow). The Release control is similarly specified, and ranges from 4000dB/s (fast) to 10dB/s (slow).

There is also an automatic mode which adjusts the attack and release times according to the input signal dynamics, and this is activated with a button located between the attack and release controls. An LED is provided to indicate when this mode is active. Essentially, the greater and faster the input signal exceeds the threshold, the faster the attack and release times — which maintains the subjective impression of loudness while exerting a degree of dynamic control.

Photo: Mark Ewing

The last control sets the threshold for the peak limiter, and this spans +4dBu at the lowest to Off at the highest, the latter corresponding to +24dBu, which is the internal clip level of the unit's signal path. Like other Dbx units, the limiter uses Instantaneous Transient Clamp circuitry to provide a soft clipping function which controls transient peaks to within 2dB over the threshold value. The limiting accuracy can be further improved by switching in Peak Stop Plus, which works by intelligently monitoring the rise time of transient input signals and predicting the likely peak level. This information is used to introduce an appropriate level of gain reduction via the compressor's VCA with the aim of preventing the transient exceeding the Stop Level threshold.

To the left and right of the three lower rotary controls are two more buttons with indicator LEDs. The one on the left activates the side-chain's external return signal path, enabling frequency-conscious compression, level ducking, and the like. To the right of the Stop Level control is a bypass button which connects the input sockets directly to the output sockets via a relay.

The VU meter to the right of the main control section can be switched to display one of three signals: input, output, or gain reduction. The first two relate to the conventional logarithmic VU scale shown by the upper markings in the meter. In both cases, 0VU corresponds to the input level selected on the rear panel (either +4dBu or -10dBV), and the output meter signal is taken after the Output Gain control and peak limiter, so shows the true output level from the unit. The gain-reduction display relates to the lower linear meter scale, calibrated from zero at the right hand side to -30dB at the left.

Located in a separate control strip between the two channels of the 162SL are two more LEDs — both larger than the rest — plus a large button. The top LED illuminates when the power is switched on, while the other is related to the button which engages the stereo-link mode. With the button pressed, the right-hand channel controls and LEDs are disabled and the left-hand controls act as masters for both channels. Having said that, the right-hand channel Bypass, Side Chain Return, and Meter Selection buttons remain operational. The side-chain signals from both channels are summed and used to generate a VCA control signal which is applied equally to both channels to prevent image shifting under compression.

In Use

The Dbx 162SL is every bit as classic a compressor as the flagship 160SL, with the same basic signature sound characteristics and flexibility. While it cannot match the 30dBu of headroom provided by the 160SL, it is still a very competent and professional product — and the +24dBu clip point is more than enough for most applications.

As on its more expensive sibling, the controls have a well-built and solid feel to them, and the control layout is ergonomic and intuitive. The inclusion of status LEDs for every function makes it easy to see at a glance what is going on, and the Threshold 'traffic lights' are extremely effective. The purple paint job and silver knobs certainly make the unit stand out in the rack, although the relatively large control knobs tend to mask the relatively small legends under each control. If you mount the 162SL in a floor rack, expect to have to kneel on the floor a lot until you are familiar with the control layout!

Setting the 162SL up with programme-dependent attack and recovery times, and with the Overeasy compression slope switched in provides the classic Dbx compression sound — and that's about as silky smooth and effortless as it gets. Treating rock vocals in this way provides delicious results. The effect is very flattering, with no unpleasant artefacts, and the unit takes ludicrous dynamic changes in its stride. Bass guitars and acoustic basses are handled with equal aplomb — affording firm control but without trampling over the source's character in the way some lesser VCA compressors can. In many ways, the 162 shares much of the character and range of a good opto-compressor, but with the additional control, precision, and stereo stability of a good VCA unit.

The 162SL may not provide the kind of pure sonic transparency that mastering houses often require from their compressors, but this unit is really intended more for tracking and mixing, working with individual instruments and sources to help polish their contributions to a mix, rather than for enhancing complete and complex mixes.

I could find nothing at all to catch out the sophisticated automatic attack- and recovery-time system — although having the facility to set times manually can also be useful. However, great care is needed here, as the unit boasts extremely fast attack and recovery times at extreme settings, both of which can lead to significant distortion if set inappropriately, potentially causing transient distortion in the case of the fastest attack time, and a kind of waveform-following release distortion for basses and other low-frequency signals.

The Peak Stop Plus limiter is a useful safety feature, but it should be set up only to catch the extreme transients. The design is not well suited to continuous hard limiting applications, and I found I could get far better and more transparent results using the compressor section with a very high ratio. When pushed hard, the Peak Stop Plus limiter tended to 'bounce' the levels in a way that suggested a slight over-limiting effect — although this was largely inaudible when used as intended to catch isolated transients.

The 162SL provides the sound of the class-leading 160SL in a more cost-effective format, while giving surprisingly little away in terms of flexibility or features. The technical compromises necessary to achieve the new UK price point all appear to be in areas that have little impact on the sonic character of the unit. Few people would ever notice the 6dB reduction in headroom, for example, and the noise performance is only a decibel worse!

In Paul White's review of the 160S, he questioned whether that machine's emphasis on superb sonic quality was actually necessary — and I have to say that for most people, most of the time, it probably isn't. The 160SL is a fabulous flagship product which I'm glad exists, but the new 162SL gets the same job done to virtually the same standards. As a tracking and mixing compressor, the 162SL does all that is required, with intuitive controls and very flexible operation, all in a more cost-effective package.